Man has become more dependent on technology in all arenas of life. The ubiquitous use of mobile technologies requires that constant electrical power, presently provided by batteries, is available. Total dependence on batteries is problematic because short battery lifespan requires larger batteries, and battery weight can become a significant issue. In the case of the military, carrying batteries becomes a backbreaking load (packs weigh in excess of 80 lbs) which limits the time soldiers can remain in the field. A device that could generate significant electrical energy to recharge batteries while one is on the move, would provide greater freedom and operational ability.
Energy “harvesting” from body movements requires the capture of mechanical energy and conversion into electrical energy. The key requirement for many electrical energy-generating technologies, such as electroactive polymers, is the ability to produce movement against a load (i.e., provide the mechanical work that will be converted to electrical energy). Up to now, attempts to extract such energy have been extremely limited in terms of wattage (i.e., 10-20 milliwatts). For example, a watch that stays powered by arm movements generates on the order of only a few thousandths of a watt or less. Because the work done by muscles during locomotion is generally inaccessible, most attempts at harvesting mechanical energy have focused on harvesting energy from shoes by, for example, placing piezoelectric devices in shoes. For example, Drake describes such a device in “The Greatest Shoe on Earth,” Wired, February 2001, pp. 90-100. Unfortunately, the only place that is relatively accessible, the foot, is a relatively poor location for extracting mechanical energy because very little mechanical work is done at the foot during locomotion.
More recently, Pelrine et al. suggested in published U.S. patent application Ser. No. 2001/0035723 that electroactive polymer devices could be used to generate electrical energy by converting mechanical energy generated during by heel strikes during walking into electrical energy. Pelrine et al. also suggested that such polymer devices may be used to convert the up and down motion of a backpack into electrical energy. However, Pelrine et al. offer no suggestions as to how to design such a backpack device. Pelrine et al. also do not recognize that a suspended load leads to controlled up/down movement and reduced stress on the wearer's shoulders as well as on the rest of his or her body.
Accordingly, there remains a strong need to develop a device capable of harvesting energy on the order of watts, particularly for military applications.
Heavy backpack loads are known to lead to spinal injuries, particularly in children. Many school districts encourage parents to purchase spare sets of books for their children to minimize the weight of backpack loads. Of course, this approach is quite expensive. Recently, wheels have been added to backpacks so that the backpacks may be pulled along the ground, thereby reducing the load on the user's back. Such designs are problematic since they do not provide much assistance when the user has to cross grass or more difficult terrain. An improved way to reduce load on the wearer's back is desired.
Another recent approach to the problem of heavy backpacks is suggested by Duckworth in U.S. Pat. No. 6,619,523, whereby a shock absorber system is applied to the backpack to take the jolts out of hitting the ground. In particular, a damper (air piston) is added to the frame of the backpack to reduce the movements of the load with respect to the pack frame. Unfortunately, Duckworth did not address the physics of walking or running with a backpack and simply built classic shock absorbers. Their springs are too short in length and too stiff to permit the large relative movements between the frame and the load which are necessary to keep the load relatively still with respect to the ground. Accordingly, rapid movement with the backpack taught by Duckworth would cause the generation of a very large force which would limit the relative movement between the load and the frame resulting in high shoulder loading as well as potentially causing the wearer to lose his or her balance.
Accordingly, there remains a strong need to develop a device capable of minimizing load stresses on the shoulders on the wearer of a conventional backpack. The present invention is designed to address these needs in the art.